Millivolt damper control device

ABSTRACT

A millivolt damper control device comprises a damper movable between a closed position where a flue is blocked and an open position, a thermoelectric device having an input voltage, a battery having a voltage, and a controller comprising a comparator circuit which compares the input voltage with a reference voltage based upon the voltage of the battery. When the input voltage is greater than or equal to the reference voltage, the comparator circuit transmits a damper signal to move the damper to the open position.

RELATED APPLICATION

This application claims priority benefit of U.S. provisional patent application No. 60/568,003 filed on May 4, 2004.

FIELD OF THE INVENTION

This invention relates to a device for controlling a damper, and more particularly to a damper control device for a fireplace.

BACKGROUND OF THE INVENTION

Many homes today have fireplaces where a flue in a chimney connects the outside air to the fireplace. Such a connection can result in leakage of air into the home. A damper can be positioned in the flue and used to keep the air out. The damper is movable between a closed position which prevents air from leaking into or out of the home, to an open position which allows air to flow and exhaust products of combustion to flow out of the home. Such known dampers are controlled by a chain, handle, lever or the like. An operator has to remember to open the damper prior to starting a fire in the fireplace, or else the products of combustion would become trapped in the home.

The products of wood fireplaces can include soot and smoke. Soot and smoke are visible, and if a wood fireplace had a damper which was closed, it would become immediately apparent that the damper was closed upon combustion of the wood. However, the products of incomplete gas combustion can be invisible and toxic (CO₂, CO, for example). Because of this potentially hazardous situation, ventilation of air has been required for gas fireplaces where dampers have been used. That is, the damper had to be permanently blocked open. Further, in some places dampers were not allowed to be used in combination with gas fireplaces.

U.S. Pat. No. 6,257,871 B1 to Weiss et al discloses a highly efficient damper control device particularly useful for gas appliances which regulates air flow in a furnace using the power of generated by a thermopile in a pilot light. However, fireplace dampers may be subjected to significantly higher load requirements than dampers in furnaces. Further, for fireplace dampers, resistive losses increase with the increased distance between the pilot light and the damper. It would be desirable to provide a damper control device for a fireplace with a thermopile providing power to the damper and to the gas valve without relying on power from a utility or land based power source.

SUMMARY OF THE INVENTION

In accordance with a first aspect, a millivolt damper control device comprises a damper positioned in a flue, wherein the damper is movable between a closed position where the flue is blocked and an open position, a thermoelectric device having an input voltage, a battery having a voltage, and a controller comprising a comparator circuit which compares the input voltage with a reference voltage based upon the voltage of the battery. When the input voltage is greater than or equal to the reference voltage, the comparator circuit transmits a damper signal to move the damper to the open position.

From the foregoing disclosure and the following more detailed description of various preferred embodiments it will be apparent to those skilled in the art that the present invention provides a significant advance in the technology and art of damper control devices. Particularly significant in this regard is the potential the invention affords for providing a high quality damper control device for fireplaces and other outside and remote applications. Additional features and advantages of various preferred embodiments will be better understood in view of the detailed description provided below.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective schematic view illustrating a chimney incorporating a millivolt damper control device in accordance with a preferred embodiment.

FIG. 2 is a perspective view of the damper, showing a battery and circuit board with a comparator circuit.

FIG. 3 is a perspective view of the cam and switches that the cam contacts as the damper motor rotates, providing information to the comparator circuit about the position of the damper.

FIGS. 4-10 are schematic and block circuit diagrams showing stages of a call for fire at the fireplace.

It should be understood that the appended drawings are not necessarily to scale, presenting a somewhat simplified representation of various preferred features illustrative of the basic principles of the invention. The specific design features of the damper control device as disclosed here will be determined in part by the particular intended application and use environment. Certain features of the illustrated embodiments have been enlarged or distorted relative to others to facilitate visualization and clear understanding. In particular, thin features may be thickened, for example, for clarity of illustration. All references to direction and position, unless otherwise indicated, refer to the orientation illustrated in the drawings.

DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS

It will be apparent to those skilled in the art, that is, to those who have knowledge or experience in this area of technology, that many uses and design variations are possible for the damper control device disclosed here. The following detailed discussion of various alternative and preferred features and embodiments will illustrate the general principles of the invention with reference to a damper control device for a gas fireplace. Other embodiments suitable for other applications, such as wood burning fireplaces, will be apparent to those skilled in the art given the benefit of this disclosure.

Turning now to the drawings, FIG. 1 shows a chimney 10 having a fireplace 12, a flue 14 which receives products of combustion from the fireplace, and a damper 20. In the preferred embodiment shown here, the fireplace 12 is a gas fireplace, with the gas supplied by a gas line 29. The damper 20 is movable by electric motor 44 via rotatable shaft 34 between a closed position where it prevents outside air from flowing down into the flue and from there leaking into a house, to an open position (as shown in FIG. 1) where the products of combustion can escape to the outside. A thermoelectric device such as thermopile 31 is positioned in a pilot light and provides sufficient electrical power to control a solenoid actuated gas valve 28. A controller 41 controls the position of the damper 20 and the gas valve 28, and comprises the circuit board 46 positioned near the damper 20, preferably at least partially within a box 30 to shield it from the elements. Wiring 22 electrically connects the circuit board 46 and the gas valve 28, and wiring 23 electrically connects the gas valve with the thermoelectric device. Diagnostic information about the status of the various elements of the millivolt damper control device may be displayed at status module 16.

The damper 20 is installed in the flue 14. FIG. 2 shows the damper 20 positioned in a damper pipe, drive motor 44 (preferably a DC electric motor) and accompanying circuit board 46 positioned in a preferably weatherproof damper control box (partially removed). To rotate the damper between open and closed positions, the rotatable shaft 34 operatively connects the drive motor and the damper. As the flue can get quite hot during operation of the fireplace, the rotatable shaft serves to space the drive motor and electronic controls away from the flue and damper pipe. Also, shaft 34 is preferably at least partially enclosed by the box 30 to protect the shaft from weathering, dirt, etc. A portion 37 of the damper pipe 32 may extend beyond a mounting member 36, shown in FIG. 2 as a ring-like structure. The portion 37 is adapted to fit inside the flue 14, and mounting brackets 38 are adapted to receive bolts that would fit into the chimney, thereby securing the damper 20 and damper pipe 32 to the chimney.

Any one of several control devices may be used to turn the fireplace fire on and off. For example, an on/off switch 25 may be provided (shown in FIG. 1). Alternatively or in conjunction with switch 25, a temperature control may be used, so that the fireplace fire is ignited when the temperature in the room drops below a predetermined level. Also an on/off switch or thermostat control could be incorporated into a handheld wireless or remote device.

In accordance with a highly advantageous feature, power to control the position of gas valve 28 is derived from the thermoelectric device, and typically is in the millivolt (less than 1 volt) range. Preferably the battery 24 (and not the thermopile) provides electrical power to run the damper motor and to the circuit board 46.

The controller 41 has a comparator circuit 40 which is used to open or close the blade(s) of the damper based on an electric signal from the external control (thermostat, manual switch, etc.). FIG. 3 shows a cam 52 which rotates with the output shaft 34 in response to rotation of the motor 44. The cam 52 has a series of ramped surfaces that engage limit switches 60, 62, 64. The switches 60, 62 and 64 activate throw contacts S4, S2, S3, respectively, on printed circuit board 46. These throw contacts on the circuit board correspond to the respective switch position, and in turn the switch positions indicate the relative position of the damper. In this way, information is provided to the controller to control the position of the damper and the gas valve, and to provide a damper status signal indicating whether the damper is in the open position or closed position.

Controller 41 allows the damper to be controlled by the typically low millivolt power (e.g. 500-600 mV) supplied by the fireplace thermopile 31, while relying on voltage from the battery for operation. FIGS. 4-10 show schematic diagrams of the circuit for the operation of the millivolt damper control device. In response to rotation of the cam 52 the various switches are thrown and the corresponding throw contacts S2, S3 and S4 switch between the normally closed contacts 71, 74, 77 and the normally open contacts 72, 75, 78. In FIG. 4, the device is in stand-by mode, motor 44 is inactive, gas valve 28 is closed so the fireplace fire is off (except for a pilot light), and throw contacts S2, S3, and S4 are shown each electrically connected with between a common contact 70, 73, 76 and a corresponding normally closed contact 71, 74, 77. Power for the comparator circuit 40 is supplied by the on-board battery 24. Preferably the battery supplies at least 3.6 VDC. A battery with suitable power, voltage and durability characteristics is a 3.6 V D-Cell battery made by Tadiran of Israel.

Contact 2 is electrically connected with contact 1 in the comparator circuit 40, but since S2's common contact 70 is not electrically connected to 72 the circuit is open. In this condition the comparator circuit 40 is awaiting a call for a fire, and no voltage is applied across the motor 44 or across solenoid actuated gas valve 28.

FIG. 5 shows the electrical connections made when an operator desires a fire at the fireplace. A Call For Fire begins when switch 25 (or other suitable controller) is thrown and contact 125 is closed, generating a fireplace signal to open the gas valve. Prior to this occurring, however, the damper 20 is sent a call to move to the open position. The comparator circuit 40 ensures that the damper is in the open position before the gas valve is opened. The comparator circuit 40 compares a reference voltage from the battery 24 (between contacts 2 and 4) with an input voltage from the thermoelectric device 31 (between contacts 6 and 4). If the input voltage from the thermoelectric device exceeds the reference voltage, then the device is considered to be receiving power from the thermopile 31. In that case, the comparator circuit contact 2 connection is switched to contact 3, closing the circuit to allow a voltage to be applied at motor 44. Preferred thermopile voltage is at least 80 mV and typically less than 1V. That is, reference voltage is at least 80 mV, so comparator circuit will supply voltage to the motor when the input voltage meets or exceeds 80 mV.

The motor 44 rotates, rotating the cam 52 with it until the switches are tripped and the contacts S2, S3 and S4 thrown as shown in FIG. 6. Switching S2 into contact with normally open contact 72 (which coincides with the damper reaching the open position) opens the circuit supplying power to the motor, stopping the motor. S3 and S4 are now switched into contact with 78 and 75, respectively. These throw contacts are redundant, and when both are closed, a voltage generated by the thermopile 31 may be applied to the gas valve 28, opening the valve and starting a fire at the fireplace. Thus, the fire is only started after the damper has been moved to the open position.

FIG. 7 shows switch 125 moved to an open position, indicating that switch 25 or the like has been turned off. The input signal is removed and Shut Off begins as power is cut to the gas valve 28. The comparator 40 detects the drop in voltage and advantageously initiates a time delay, allowing products of combustion time to leave the flue.

In FIG. 8, the time delay has ended. Comparator circuit contacts 2-3 are switched to 2-1, applying voltage across the motor 44 to move the damper to the closed position. The cam surfaces may be staggered so that the switches/throw contacts are reset at different times. For example, S3 may be returned first, reconnecting contact 76 with 77, as shown in FIG. 9. Next, S4 may be returned, reconnecting contact 73 with 74 as shown in FIG. 10. Finally, S2 may be returned, returning the controller to Stand-By Mode as shown in FIG. 4.

In accordance with a highly advantageous feature, the comparator circuit 40 may ignore the input voltage for a period of time between the end of the time delay and the time when S4 has reconnected between 73 and 74. This prevents the damper from getting stuck during the period of time when it is returning to the closed position if the input signal is reintroduced.

From the foregoing disclosure and detailed description of certain preferred embodiments, it will be apparent that various modifications, additions and other alternative embodiments are possible without departing from the true scope and spirit of the invention. The embodiments discussed were chosen and described to provide the best illustration of the principles of the invention and its practical application to thereby enable one of ordinary skill in the art to use the invention in various embodiments and with various modifications as are suited to the particular use contemplated. All such modifications and variations are within the scope of the invention as determined by the appended claims when interpreted in accordance with the breadth to which they are fairly, legally, and equitably entitled. 

1. A damper control device comprising, in combination: a damper movable between a closed position and an open position; a thermoelectric device; a battery having a voltage; and a controller comprising a comparator circuit which compares an input voltage from the thermoelectric device with a reference voltage based upon the voltage of the battery; wherein when the input voltage is greater than or equal to the reference voltage, the comparator circuit transmits a damper signal to move the damper to the open position.
 2. The damper control device of claim 1 further comprising an electric motor having a rotatable shaft operatively connected to the damper which moves the damper between the open position and the closed position; wherein the damper signal comprises application of the reference voltage across the motor.
 3. The damper control device of claim 1 wherein the battery supplies electric power to a motor which moves the damper and to the comparator circuit.
 4. The damper control device of claim 1 wherein the battery is mounted on a box which also houses the comparator circuit.
 5. The damper control device of claim 1 wherein the comparator circuit applies a voltage to open a gas valve to initiate combustion when a fire is desired at a fireplace, and removes the voltage to close the gas valve and terminate combustion when a fire is no longer desired at the fireplace.
 6. The damper control device of claim 5 wherein when the fire is desired at the fireplace, the comparator circuit opens the gas valve after receiving a damper status signal indicating that the damper is in the open position.
 7. The damper control device of claim 1 wherein the comparator circuit maintains a predetermined time delay corresponding to a time between when the input voltage is removed from the comparator circuit and when the reference voltage is reapplied at the motor.
 8. A damper control device comprising, in combination: a damper; a motor which moves the damper between a closed position and an open position; a thermoelectric device; a battery having a voltage; and a controller comprising a comparator circuit which compares an input voltage from the thermoelectric device with a reference voltage based upon the voltage of the battery; wherein the comparator circuit maintains a predetermined time delay corresponding to a time between when the input voltage is removed from the comparator circuit and when the reference voltage is reapplied at the motor.
 9. The damper control device of claim 8 wherein power to run the motor is supplied by the battery, and power to move the gas valve is supplied by the thermoelectric device.
 10. The damper control device of claim 8 wherein power to run the comparator circuit is supplied by the battery. 